Superfetch is an attribution to thrashing, not the sole reason for thrashing.
While you may not hear it because you have your case at your feet next to a desk, and you most likely use a single 7200RPM hard drive, you can certainly notice it with several 10,000RPM-15,000RPM hard drives when your case is on top of your desk next to you.
You're lowering the lifespan of your hard drive(s) significantly by constantly loading apps into memory which you may not even use.
While it does load commonly used applications, "commonly used" doesn't literally imply often used, but more along the lines of whether you've ran the application at all and after a certain time span it theoretically deletes it from the prefetch list.
I suppose you could argue to say it may make more of an impact for people with 5400RPM hard drives but I'd disagree for 7200RPM and beyond.
I doubt many people who use a 5400RPM hard drive have access to much ram to begin with though, so this is something else to consider.
Yes, you caught my 'trashing' typo, my bad.
Firefox has the tab restoration feature as well, and you can also exit Firefox with your tabs open and it'll restore them for you, not that this has anything to do with the subject at hand.
You're slowing system performance by using any pagefile at all with 6GB of a ram, that's more than enough.
Technically if you wanted a pagefile though you'd want to set it to 9216MB going by Microsoft's formula of 6144MB x1.5 = 9216MB for improved use of the pagefile system.